1. Field of the Invention:
This invention relates to a shield type tunneling machine, and more particularly, to a shield type tunneling machine adapted to use in a pipe jacking method for thrusting a pipe in the ground.
2. Description of the Prior Art:
In a pipe jacking method, as disclosed in U.S. patent Ser. No. 4,311,411, is disposed a shield type tunneling machine in the foremost portion of a plurality of pipes to be thrusted. While a tunnel face is excavated by the operation of a rotary cutter head provided in the tunneling machine, a thrust is given to said pipe and the fore tunneling machine by a thrusting jack provided in a shaft and adjacent the rearmost pipe. Therefore, both the pipe and the tunneling machine are thrusted in the ground excavated by the operation of said cutter head.
The rotary cutter head is disposed spaced ahead from a diaphragm crossing the interior of a shield body, and debris excavated from a face during thrusting of said tunneling machine and pipe enters and fills a front area between said cutter head and said diaphragm through said cutter head. The debris filling said front area of the diaphragm serves to transmit the earth pressure on the face to the diaphragm of the shield body and the reaction of the diaphragm to the face so that the face is stably maintained without collapse or upheaval by balance between the reaction and the earth pressure.
Conventionally, the debris is rotated with said cutter head in the front area of said diaphragm and directed toward a discharging means such as a screw conveyer provided on a lower portion of said diaphragm and discharged through the discharging means to the rear of the diaphragm. However, a large frictional force works between the rotating debris and said diaphragm so that large torque is needed for the rotation of said cutter head. Thus, the provision of a compact drive unit for the cutter head and a compact shield type tunneling machine for a pipe jacking method is hindered, i.e. the provision of a small diameter shield body is difficult.
While the reduction of frictional force between the debris and the diaphragm has to be considered particularly during the excavation and thrusting in the gravel ground, an embodiment of effective method of reducing the friction was conventionally executed in which pressurized high concentration muddy water is applied to the face to stabilize the face and give fluidity to the debris. However, the use of the pressurized muddy water needs the subsequent treatment of muddy water mixed with debris, and further the treatment presents problems concerning installation, cost or the like. In addition, said frictional force is increased in proportion to pressure exerted to the debris filling the front area of said diaphragm. Therefore, the pressure needs to be reduced as small as possible for reducing the frictional force. However, since the pressure acting on the debris cannot be reduced lower than the active earth pressure of the face ground to stabilize the face, the reduction of said frictional force by the lubricating action of the muddy water was naturally limited.